The invention relates to a method for connecting a user equipment to a network device via a mobile communication network wherein the user equipment comprises at least a deregistered state and a registered state, wherein the deregistered state comprises at least two substates, a normal and an attempting-to-attach substate, for defining a connectivity state of the user equipment to the mobile communication network, and wherein the user equipment is connectable to the mobile communication network and wherein the network device is connected to the mobile communication network
comprising the steps of                a) Paging of the user equipment by a paging signal using a, preferably unique, user equipment identifier,        b) Switching to the attempting-to-attach substate of the deregistered state of the user equipment when receiving a paging signal,        c) Attaching the user equipment to the mobile communication network, and        d) Switching to the registered state of the user equipment depending on a result of the attachment according to step c).        
The present invention also relates to a system for connecting a user equipment to a network device via a mobile communication network, wherein the user equipment is formed such to provide at least a deregistered state and a registered state, wherein the deregistered state comprises at least two substates, a normal and an attempting-to-attach substate, for defining a connectivity state of the user equipment to the mobile communication network, and wherein the user equipment is connectable to the mobile communication network and wherein the network device is connected to the mobile communication network, and wherein the user equipment is formed such that on receiving a paging signal due to paging using a, preferably unique, user equipment identifier, the user equipment switches to the attempting-to-attach substate of the deregistered state of the user equipment, attaches to the mobile communication network, and switches to the registered state of the user equipment depending on a result of the attachment according to step c).
Conventional connecting techniques in mobile communication networks, for example a cell phone connecting to a base station of a UMTS mobile communication network and further for example via the UMTS mobile communication network and the internet to a dedicated server, like an email server, have been mainly designed to be used by human beings.
Conventional states of a user equipment, also named mobile terminal or mobile station, comprises therefore in general two operational states in particular regarding registration, namely a deregistered state and a registered state. In addition, in registered state the user equipment can be in two different modes regarding its connection, namely an EMM-connected or an EMM-idle state. When a signalling connection is established the user equipment may be in the registered state in normal-service substate and in a further, additional substate EMM-connected. If a NAS signalling connection is not established the user equipment may be in a substate EMM-idle. When the user equipment is in the registered state, the user equipment may transmit data to respectively via the mobile communication network to a dedicated server for example in the internet. In the deregistered state the user equipment may be in normal substate or in attempting-to-attach state. In the normal deregistered substate the user equipment cannot transmit or receive data but may be able to initiate an attach or a combined attached procedure. For initiating an attach or combined attached procedure the user equipment switches in the deregistered state to an attempting-to-attach substate initiating an attach. When the attach to the mobile communication network is successful the user equipment becomes registered in the mobile communication network and switches to the registered state allowing the transfer of data between the user equipment and the dedicated server. In this normal-service registered state the user equipment may transmit data which, if the user equipment is in EMM-idle, may be initiated by a Service Request NAS signalling message.
FIG. 1 shows a conventional switching of states of a user equipment in a current 3GPP model. When the user equipment is switched on (reference sign 72) the user equipment is first in a deregistered state B. After switching on 72 the user equipment likes to become attached to a mobile communication network and therefore tries to register with the mobile communication network as soon as possible. After a successful attach (reference sign 70a) the user equipment switches from the deregistered state B to a registered state C. The user equipment also remains registered, i. e. in the normal-service substate, as long as no error condition or restriction from the mobile communication network occurs. The registration is prerequisite to reachability of the user equipment which may be defined via paging based on tracking area information stored in a mobile communication network entity, preferably a mobility management entity and the tracking area information depends on location registration of the user equipment.
However, for new classes of devices, in particular machine type communication devices, conventional registration techniques have a number of drawbacks. For example if a machine type communication device is fixed in a location and scheduled to deliver data once every month via the mobile communication network this would cause costs due to a high energy consumption of the user equipment for being and staying registered in the mobile communication network. Another drawback is that the registration of the machine type communication device creates a signalling overhead and shortens the bandwidth for other especially none-machine-type-communication devices in the mobile communication network. In the registered state the user equipment has to be permanently staying in the necessary context state for example security context, location context, bearer context, etc.
To overcome these drawbacks the user equipment may be switched on and/or off at appropriate times: The user equipment may be switched on for example when an uplink communication, i. e. from the user equipment to the mobile communication network, is necessary: The user equipment then attaches and registers to the mobile communication network and all necessary context is created subsequently. Switching on and off may be handled by local environment devices of the user equipment, for example the user equipment may be communicating with or connected to a timer, counter thresholds, sensors or the like.
Another option to overcome these drawbacks is the use of well-defined time slots for a communication, in particular for the registration process, of the user equipment with the mobile communication network. These time slots are fixed and known to the user equipment and to a predefined entity of the mobile communication network handling the establishment of the connection. This may be implemented for example by attaching the user equipment to a timer device which activates or deactivates the user equipment power switch sufficiently before and after the defined time slots. In order to obtain a reliable bidirectional connection between the user equipment and the mobile communication network the local time of the mobile communication network and the user equipment must be well synchronized.
However this solution has inter alia one main disadvantage: This solution may not be applicable to devices which need to be reachable at all times, since by turning off the user equipment the user equipment is deregistered and is not able to receive any communication signals from the mobile communication network.